1. Field of the Invention
This invention relates to a method of manufacturing a magnetic recording tape such as a magnetic tape, and more particularly to an improvement in a method of manufacturing a magnetic recording medium by heating and evaporating depositing material and depositing the vapor particles of the depositing material on a substrate material running along the outer peripheral surface of a cylindrical cooling can.
2. Description of the Prior Art
There has been a demand for increase in the amount of information to be recorded on a magnetic recording medium such as a magnetic tape and for a high tone quality and a high image quality. As is well known, in order to meet such a demand, high-density recording is necessary. A deposition magnetic tape has been recently developed as a magnetic recording medium for high-density recording and has been put into practice as "Hi8ME Tape". The deposition tape comprises a substrate such as of PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) and a ferromagnetic metal layer such as of iron, cobalt, nickel and/or the like deposited on the substrate. The deposition magnetic tape has a high effective magnetic flux density Bm, a high coercive force Hc and a large squareness ratio SQ and is excellent in the electromagnetic characteristics in the short wavelength range. Further, in the deposition magnetic tape, since the magnetic layer may be small in thickness, the recording demagnetization and the thickness loss upon playback can be effectively suppressed, and since the magnetic layer is free from intervening materials such as additives or binders unlike in the conventional magnetic tape where the magnetic layer is formed by application, the charging density of the magnetic material can be increased.
In the normal method of manufacturing the deposition magnetic tape, depositing material such as ferromagnetic metals, e.g., iron, cobalt, nickel or alloys of such metals, in a crucible is heated to evaporate by an electron beam or the like, and the vapor particles of the deposition material is continuously deposited on a high polymer film such as of PET or PEN running along the outer peripheral surface of a cylindrical cooling can between a position where the vapor particles impinge upon the film at a large angle and a position where the vapor particles impinge upon the film at a small angle.
To further improve the coercive force Hc of the deposition magnetic tape is important to increase the playback signal output.
Accordingly there have been proposed various methods for improving the coercive force Hc of the deposition magnetic tape.
For example, Japanese Patent Publication No. 2(1990)-27732 says that the coercive force Hc of the deposition tape can be improved by forming an oxide layer on a magnetic layer of cobalt-nickel alloy by blowing oxidizing gas such as O.sub.2 gas on the depositing portion of the high polymer film from a position near the position where the vapor particles impinge upon the film at a small angle.
Further it has been known that the coercive force Hc can be improved by increasing the minimum incidence angle (the minimum value of the angle at which the vapor particles impinge upon the film).
However when oxidizing gas such as O.sub.2 gas is blown on the depositing portion of the high polymer film, the thickness of the oxide layer increases as the amount of the oxidizing gas blown on the film increases though the coercive force Hc increases with increase in the amount of the oxidizing gas. The oxide layer intervenes between the magnetic layer and the magnetic head for recording and playback, which results in lowering of output.
Further when the minimum incidence angle of the vapor particles is increased, the depositing efficiency lowers and the adhesive force of the vapor particles to the high polymer film deteriorates with increase in the minimum incidence angle. For example, when the minimum incidence angle is increased from 45.degree. to 60.degree., the depositing efficiency lowers by not less than 50%.